1. Field of the Invention
The present invention relates to a perovskite oxide of novel composition with A-site including Bi and B-site including Fe. The invention also relates to an oxide composition, oxide body, piezoelectric element, and liquid discharge apparatus using the same.
2. Description of the Related Art
Provskite oxides having ferroelectricity are used in various applications, such as piezoelectric elements, switching elements, and the like. For example, as a perovskite oxide having a good piezoelectric property, lead zirconate titanate (PZT) is known. PZT is a ferroelectric body having spontaneous polarization in the absence of electric field, and said to show a high piezoelectric performance at and near a morphotropic phase boundary (MPB). If environmental burden is considered, it is preferable that Pb content is reduced as much as possible and a non-lead system that does not include Pb is more preferable. In non-lead perovskite oxides, development of new materials showing a higher piezoelectric performance has been in progress.
In developing new non-lead system materials, it is noteworthy that some of the perovskite oxides presumably having high characteristics in theory can be turned into perovskite oxides by sintering under a high pressure exceeding several GPa, although they can not take a perovskite crystal structure by high-temperature sintering under normal pressure. For example, Bi-system perovskite oxides are considered in theory to be non-lead system piezoelectric materials having a high piezoelectric property (ferroelectric property), but most of them hardly, some of them can not, take a perovskite-type structure by high-temperature sintering under normal pressure.
Currently, in bulk ceramics, only BiFeO3 can be manufactured into a Bi-system perovskite oxide under normal pressure. For example, it is reported that BiAlO3 can be turned into a bulk ceramic only by a high-temperature and high-pressure synthesis of 6 GPa with 1000° C in a literature by J. Zylberberg et al., “Bismuth Aluminate BiAlO3: A New Lead-free High-Tc Piezo-/ferroelectric”, ISAF 2007 proceedings, 28PS-B13 (Non-Patent Document 1). Sintering under a high pressure, however, requires a complicated system and the process is not straightforward.
In the mean time, device downsizing has been underway in the trend toward high density and high integration of devices. Also, in the field of piezoelectric elements, thickness reduction of elements has been moved forward, and perovskite oxide films capable of providing favorable element property have been studied for that purpose.
BiFeO3 has been studied for the application to ferroelectric memory (FeRAM) or piezoelectric actuator because it has an excellent ferroelectricity. BiFeO3 is also a magnetic body and has been drawing attention as a multiferroic material. Ti doped BiFeO3 is reported in a literature by Y. Wang and C. W. Nan, “Enhanced ferroelectricity in Ti-doped multiferroic BiFeO3 thin films”, APPLIED PHYSICS LETTERS, Vol. 89, pp. 052903-1-052903-3, 2006 (Non-Patent Document 2) and in a literature by L. Hongri and S. Yuxia, “Substantially enhanced ferroelectricity in Ti doped BiFeO3 films”, J. Phys. D, Appl. Phys., Vol. 40, pp. 7530-7533, 2007 (Non-Patent Document 3).
It has been attempted to produce a perovskite-type crystal structure in a Bi system oxide that can not take a perovskite-type crystal structure unless sintered under a high pressure by mixing it with BiFeO3 that takes a perovskite-type crystal structure relatively easily at bulk sintering under normal pressure and in film state to form a solid solution. A Bi (Fe, Al)O3 film of perovskite structure, in which 0 to 50 mol % of BiAlO3 is solidified with BiFeO3 on a SrTiO3 substrate, is reported in a literature by M. Okada et al., “Synthesis of Bi (FexAi1-x)O3 Thin Films by Pulsed Laser Deposition and Its Structural Characterization”, Japanese Journal of Applied Physics, Vol. 43, No. 9B, pp. 6609-6612, 2004 (Non-Patent Document 4). Further, a Bi(Fe, Co)O3 film of perovskite structure, in which 0 to 33 mol % of BiCoO3 is solidified with BiFeO3 on a SrTiO3 substrate, is reported in a literature by S. Yasui et al., “Crystal Structure Analysis of Epitaxial BiFeO3—BiCoO3 Solid Solution Films Grown by Metal organic Chemical Vapor Deposition”, Japanese Journal of Applied Physics, Vol. 46, No. 10B, pp. 6948-6951, 2007 (Non-Patent Document 5).
As a non-lead perovskite oxide, barium titanate (BaTiO3) is known. Japanese Unexamined Patent Publication No. 2007-287745 (Patent Document 1) discloses a perovskite oxide in which BiFeO3 is solidified with BaTiO3. The perovskite oxide described in Patent Document 1 is represented by the expression below.(Bi1-x, Bax)(Fe1-X, Tix)O3 
where, 0<x<1, and in Examples, the film forming is performed within the range, 0.05≦x≦0.60 (claim 1 and Paragraph 0060 in Patent Document 1).
The present invention has been developed in view of the circumstances described above, and it is an object of the present invention to provide, in a system with A-site including Bi and B-site including Fe, a perovskite oxide of novel composition with an excellent ferroelectric performance (piezoelectric performance).